Coupling for multi-walled lines

This application claims the benefit of priority from European Patent Application No. 233 052 05.9, filed on Feb. 15, 2023, the entirety of which is incorporated for reference.

The present disclosure relates to a plug-in coupling for multi-walled flexible lines, also known as a “Johnston coupling”. Multi-walled flexible lines include in particular vacuum-insulated lines but also lines in which the space between the walls or pipes of the lines is filled with air, an inert gas, or a medium for temperature control of the line.

Cryogenic media, also known as cryogenic fluids, are often transported on ships, in tanker wagons or on tanker trucks. Important examples include liquefied natural gas (LNG), which has an evaporating temperature of −162° C. (111 K), liquid nitrogen with an evaporating temperature of −196° C. (77 K), liquid hydrogen (evaporating temperature −253° C., 20 K) or liquid helium (evaporating temperature −269° C., 4 K). The transfer from one tank to another during loading is typically accomplished with vacuum insulated lines and couplings.

For transfer purposes, the transfer lines are designed to be flexible and are provided at least at one end with a rigid so-called Johnston coupling, with which two cryogenic lines can be detachably connected without interrupting the thermal insulation at the connection point.

For the transfer the transfer lines are coupled to tanks to be connected, subsequently rendered inert by purging, and cooled down to operation temperature. Before decoupling the transfer line is warmed up to ambient temperature and rendered inert. During the complete operation the couplings must be tight against the environment while the temperature of components of the coupling varies between ambient and cryogenic temperatures.

A Johnston coupling is disclosed, for example, in EP 1 957 851 B1 and is shown in. A first sealseals the two coupling halves against each other in the cold area. A second sealseals the two coupling halves against each other in the warm area. This creates a dead space between the two seals. When the coupling is warm, the second sealprimarily seals the two coupling halves against each other. When the coupling is cold, the first sealprovides the primary seal and the second sealserves as a redundancy.

In simple terms, in a Johnston coupling two rigid double-walled vacuum-insulated coupling parts,are inserted into each other. The inner diameters of the coupling parts are typically between 10 mm and 200 mm. In principle, however, smaller or larger inside diameters are also possible. The male coupling partis plugged into the female coupling part. The male and female coupling parts are also referred to as coupling plugand coupling socket.

Since the first sealonly works properly when it is cold, the exact distance between the first and second seal is crucial for the correct operation of the first seal. Slight deviations due to manufacturing tolerances will result in permanent leakage of one or the other seal. Therefore, manufacturing tolerances are quite tight which increases the production costs.

The two seals,create a dead space between the male coupling part and the female coupling part, in which a certain amount of cryogenic fluid is accumulated and captured during cooling because the sealis not completely tight at the beginning of the cooling process. The amount of captured cryogenic fluid cannot be completely removed from the dead space when the coupling is in its coupled state. Therefore, the captured cryogenic fluid enters the environment during uncoupling of the coupling parts. If the fluid is hazardous, e.g. inflammable, toxic etc., this will pollute the environment and imperil the operators of the transfer line.

In the context of the present application the term fluid is to be understood as any kind of flowable material that can have a solid, liquid, or gaseous state of aggregation. In this sense fluids also include solid powders that can be pumped and flow through transfer lines like a liquid. Furthermore, fluids also include aerosols and emulsions.

The described double-walled vacuum insulated line is taken only as an example for other types of multi-walled lines mentioned above. Conventional couplings for multi-walled lines frequently have the problem that they are not gas tight when the coupling has not yet reached its operation temperature which entails the problems described above.

In the context of the present application the term tube, pipe or line is to be understood as conduct with any kind of cross-sectional shape.

In view of the limitations of existing couplings there remains a desire for an improved coupling to overcome or at least improve one or more of the problems mentioned at the outset.

According to a first aspect the present disclosure suggests a coupling for connecting a first and a second multi-walled line each one having at least two concentric pipes, which are separated by a space. The coupling comprises a female coupling part comprising at least two concentric tubes including an inner and an outer tube each connected at one end with one of the concentric pipes of the first multi-walled line. The other ends of the at least two concentric tubes are joined in a gas tight manner. The inner tube is provided with a sealing surface. The coupling further comprises a male coupling part comprising at least two concentric tubes including an inner and an outer tube each connected at one end with one of the concentric pipes of the second multi-walled line. The other ends of the at least two concentric tubes of the male coupling part are joined in a gas tight manner. The at least two concentric tubes of the female and/or male coupling parts are compressible and/or expandable in an axial direction.

When in the coupled state the proposed coupling generates a pressure force by which a fluid tight connection between the male and female coupling part is already achieved when the coupling has not yet reached its operation temperature. I.e. the coupling is already gas tight when for instance a transfer line for cryogenic fluids is still warm. Normally, the coupling becomes fluid and/or gas tight only after it has reached its operation temperature. As a result, lose manufacturing tolerances are acceptable because the tolerances are compensated by the amount of compression and/or expansion of the male and/or female coupling part. Due to the elastic compression and/or expansion of the male and/or female coupling parts the materials they are made from can be different and can have different coefficients of thermal expansion. Therefore, the materials of the coupling parts may be chosen to adapt the coupling to specific needs.

Advantageously, the at least two concentric tubes of the female and/or male coupling are corrugated. Corrugation is a convenient way to make the concentric tubes compressible and/or expandable in an axial direction of the tubes.

In an advantageous embodiment the coupling comprises a seal that is arranged between the sealing surface of the female coupling part and a front end of the male coupling part. The seal can be made from e.g. metal, polymer or rubber. The female and/or male coupling parts being compressible and/or expandable ensure that the seal receives a sufficient axial pressure to make it fluid tight even when the coupling has not yet reached its operation temperature and in the presence of significant manufacturing tolerances.

In a useful embodiment the seal is attached to the female or male coupling part.

Advantageously, the sealing surface is angled relative to the axial direction of the inner tube. Specifically, the sealing surface can take the form of a step but other shapes such as e.g. bevel, fillet, etc. are also technically possible. Furthermore, the sealing surface, step, seal, etc. do not have to have a circular cross-section. Oval, polygonal or any cross-sectional shapes are also technically conceivable.

With advantage the female and male coupling parts comprise a flange. The flanges serve as mechanical means to firmly connect the male and female coupling part.

In an advantageous embodiment a seal is arranged between the flanges. The seal is in the warm part of the coupling and is a backup or redundancy for the seal in the cold part of the coupling. Due to the corrugation the length of the thermal path is increased. This improves the thermal insulation of the coupling simply because the thermal resistance between the seal between the sealing surface and a front face of the male coupling part and the seal between the flanges is increased. Consequently, the length of the coupling required to achieve a given level of thermal insulation may be shorter if the concentric tubes are corrugated than if they are not.

In a further embodiment of the coupling according to the present disclosure the sealing surface of the female coupling part is provided with a collar. The collar serves as a convenient holding means for a seal in the cold part of the coupling.

The collar can accommodate a tubular seal on its inner or outer perimeter. The tubular seal can be ring-shaped.

Advantageously, the tubular seal has a larger or smaller coefficient of thermal expansion than the collar. When cold fluid such as a cryogenic fluid streams through the coupling the seal shrinks more or less than the collar. When the tubular seal is fitted on the outer or inner perimeter of the collar an additional frictional connection between the collar and the seal is realized.

In useful embodiments of the coupling the space between the at least two concentric pipes of the first and/or second multi-walled line is evacuated, filled with air, or inert gas or with a medium for temperature control of the inner pipe. These embodiments are adapted to various applications in which different types of transfer lines need to be coupled.

In a preferred embodiment of a coupling according to the present disclosure the distance between the front end of the male coupling part and a contact surface of the associated connection flange is larger than the distance between the surface of the sealing surface of the female coupling part and a contact surface of the associated connection flange. Due to this arrangement the seal arranged between the sealing surface of the female coupling part and the front end of the male coupling part are always compressed even when manufacturing tolerances are present that exceed thermal expansion or shrinking of the coupling when the temperature of the coupling varies during the operation of the coupling.

According to a second aspect the present disclosure suggests a transfer device for cryogenic fluids comprising a coupling according to the first aspect of the present disclosure.

The figures are purely schematic and do not reflect real measures and dimensions of the illustrated objects.

shows a first embodiment of a couplingaccording to the present disclosure. The couplingcomprises a male coupling partand a female coupling part. The male coupling partis connected with a first vacuum insulated transfer line. The female coupling partis attached to a second vacuum insulated transfer line. The transfer lines,have an inner pipeand an outer pipe. Between the inner and outer pipes,there is an evacuated spacefor insulation purposes.

The male coupling partcomprises an inner tubeand an outer tube, which are separated by a space. The inner and outer tubes,are corrugated in a section S with the length s. The corrugated section S gives flexibility to the male coupling partin an axial direction indicated inwith a double arrow. More specifically, the male coupling partis compressible and expandable in the directions of double arrow. The inner tubeof the male coupling partis connected with the inner pipeof the first transfer line. The outer tubeis connected with a flangeon a contact surfaceof the flange. The outer pipeof the first transfer lineis connected with an opposite side of the flangein a vacuum tight fashion. The spacecommunicates with evacuated spaceof the first transfer line. As a result, vacuum insulation between the inner and outer tube,of the male coupling partis achieved. Opposite to the flangethe inner and outer tubes,are joined in a vacuum tight manner to form a front faceof the male coupling part. A length Lm of the male coupling partis defined as the distance between the front faceand the contact surfaceof the flange.

The female coupling partcomprises an inner tubeand an outer tube. Ends of the inner and outer tubes,are connected with a flange. Opposite ends of the inner and outer tubes,are connected with the inner and outer pipes,, respectively, of the second transfer line. The inner tubeforms a circular stepwhich bridges a difference between a diameter of the inner tubeto a smaller diameter of the inner pipe. In the embodiment shown inthe circular stepis an integral part of the inner tube. In other embodiments the circular stepis formed by a ring welded to the inner tube. A skilled person may conceive further ways how to create the circular step. On the circular stepa circular sealis attached. The sealhas a diameter that essentially corresponds to the diameter of the front faceof the male coupling part. The sealis made for instance from metal, polymer, or rubber. The flangecarries a circular seal. A length Lf of the female coupling partis defined as the distance between the circular stepand a contact surfaceof the flange. The length Lf of the female coupling partis for instance 1 to 3 mm shorter than the length Lm of the male coupling part. For the sake of simplicity, the thickness of the sealsandis neglected because it will lead only to a certain additional compression of the male coupling part.

In the embodiment shown inthe stepfunctions as a sealing surface for the seal. In other embodiments the sealing surface does not necessarily have to be a step. Other shapes such as bevel, fillet, etc. are also technically possible. Furthermore, the sealing surface, step, seal, etc. do not have to have a circular cross-section. Oval, polygonal and similar cross-sections are also technically conceivable.

For connecting the coupling, the male coupling partis inserted into the female coupling part.shows the couplingin its connected state. In the connected state the flangesandare tightly connected with screws or clamps (not shown in). Since Lf<Lm the corrugated section S is compressed to a length s<swhen the contact surfaces,of the flanges,are in direct contact. Due to the compression of the corrugated section S the sealis compressed already in a warm state of the coupling. As a result, the sealis fluid tight already when the couplingis coupled even before it is cooled down to the operational temperature of the coupling. In consequence, no fluid can enter the dead space enclosed by the sealand the seal. The difference of 1 to 3 mm between the length Lf of the female coupling partand the length Lm of the male coupling partis normally sufficient to compensate even lose manufacturing tolerances for the male and female coupling part,, respectively. However, it is noted that the length difference between the male and female coupling parts can be chosen smaller or larger than 1 to 3 mm in case of need and depending on a specific application.

Due to the compression of the male coupling partthe sealis fluid tight in all operating states. Therefore, the sealcould be omitted but when present, it serves as a backup in case the sealfails for any reason.

For the sake of completeness, it is noted that the sealis at the cold area of the couplingwhile the sealis in the warm area of the coupling.

In a variant of the couplingthe sealis attached to the front faceof the male coupling partwithout altering the functionality of the coupling.

Normally, the transfer lines,are flexible transfer lines with corrugated inner and outer pipes,. For the sake of simplicity, however, the pipes,are shown only schematically in the figures without exhibiting the corrugation.

illustrates a modified embodiment of the coupling. In this embodiment the circular stepis provided with a collar. The collaris a sort of continuation of the inner pipeof the transfer line. A cylindrical sealhas an inner diameter corresponding to the outer diameter of the collarand is fitted on the collar. The length of the cylindrical sealis c. The length Lm of the male coupling part, the length Lf of the female coupling partand the length c of the sealare selected such that Lf<c+Lm in an uncoupled state of the coupling. I.e. when the couplingis coupled such that the contact surfaces,of the flanges,are in direct contact the corrugated section S is compressed and exerts a pressure on the cylindrical sealsuch that the inner pipesof the transfer lines are connected in a leak tight fashion. This prevents any fluid flowing through the inner pipesfrom entering in the space between the sealsand. In addition to that, the sealis made of a material with the higher coefficient of thermal expansion than the collar. When the sealcools down when it comes into contact with cryogenic fluid flowing in the inner pipes, the sealradially shrinks more than the adjacent collarand an additional frictional connection between the collarand the sealis produced. Again, the thickness of the sealis neglected in this reasoning.

exhibits a further modified embodiment of the coupling. In this embodiment the collaron the circular stephas a diameter which is larger than the diameter of the inner pipebut smaller than the diameter of the inner tube. In this embodiment the outer diameter of the cylindrical sealcorresponds to the inner diameter of the collarsuch that the sealfits into the collar. In this embodiment the sealhas a lower coefficient of thermal expansion than the collar. On cooling, the sealshrinks less than the adjacent collarand a frictional connection is produced. Apart from that, the couplingshown infunctions in the same way as the couplingof.

In a variant of the embodiment shown in, which is not illustrated, the inner diameter of the sealcorresponds to the outer diameter of the collar. In this variant, the sealas a coefficient of thermal expansion which is larger than the coefficient of thermal expansion of the collar. In this way, when the coupling is cooled by cryogenic fluid than the sealshrinks more than the adjacent collarlike it has been described in connection with.

It is noted that in other embodiments the collaris attached to the male coupling part.

displays a further embodiment of a coupling. In this embodiment the inner and outer tube,are corrugated in a section S. The relative length of the male and female coupling parts,are the same as it has been described with reference to. the only difference between the embodiments shown inis that the female coupling partis elastically expanded or elongated for generating the force exerted on the sealby the front faceof the male coupling part. As it has been described in connection with, the sealis already leak tight from the very beginning when the couplingis brought into the coupled state and prevents any fluid flowing through the inner pipesfrom entering in the space between the sealsand.

Finally, in yet another embodiment of the present disclosure, which is not illustrated in the figures, the inner and outer tubes,,,of both the male and female coupling parts,are corrugated. When this coupling is in its coupled state then the length difference between the male and female coupling parts Lm and Lf, respectively, are compensated be a compression of the male coupling part, expansion of the female coupling partor a combination of both. As a result, the sealand, respectively, on the cold side of the coupling is already leak tight before it has been cooled down to its operational temperature. This effect is achieved by the compression and/or expansion of the male and female coupling partsand, respectively.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” does not exclude a plurality.

A single unit or device may perform the functions of multiple elements recited in the claims. The fact that individual functions and elements are recited in different dependent claims does not mean that a combination of those functions and elements could not advantageously be used.